The present invention relates to a method for the preparation of finely divided metal particles or, more particularly, to a method for the preparation of finely divided particles of a metal by the vapor-phase decomposition reaction of a vaporizable compound of the metal ignited by the irradiation with actinic rays.
Along with the progress of various modern technologies in recent years, metallic materials are required to be supplied in a finely divided particulate form. Needless to say, various methods in the prior art are known and practiced for the preparation of metal powders but none of the conventional methods can provide a metal powder to meet the requirements in the modern high technologies. A method is proposed in Japanese Patent Kokai 60-51539 according to which powders of metals can be obtained as a deposit by the vapor-phase chemical decomposition from a vaporizable compound of the metallic element. As a means to effect vapor-phase chemical decomposition of a vaporizable metal compound, use of laser beams is suggested in Chemistry and Industry, volume 15, pages 247-251 Apr. 15, 1985). This journal article, however, is directed to a subject matter of preparing a thin coating film of a metal or a compound semiconductor on a substrate surface by the method of chemical vapor deposition so that nothing is described there on the conditions by which deposit of a metal by the laser beam-ignited vapor-phase decomposition could be obtained in a finely divided particulate form.
It is generally understood in the prior art of the laser beam-induced vapor-phase decomposition of a vaporizable metal compound that a photon of the laser beam is effective on an average only to produce one or less of the metal atoms or the so-called quantum yield is very low. Therefore, the method cannot be an industrially advantageous process in respect of the prohibitively high production costs due to the great consumption of the laser beam energy or requirement of installing a very expensive high-output laser equipment in addition to the problems of the poor controllability of the reaction and contamination of the product by the by-product impurities to cause a problem in the product quality.